The 42-year-old NYPD officer loved and respected Peter Figoski, who had his back more often than anyone during the three years they spent together on the midnight shift in one of the city’s toughest precincts.

“They were like brothers,” said Estrada’s sister, who declined to give her name.

Figoski, 47, was killed in a robbery gone awry in Cypress Hills, Brooklyn, early yesterday, after he and Estrada went to the scene as backup for other cops.

Figoski took one bullet to the face after being ambushed by Lamont Pride, police said. Estrada was struggling with Pride’s accomplice at the time.

But as soon as he heard the shot, he dropped the man he was wrestling with and sprinted after Pride, chasing him several blocks before nabbing him.

Police Commissioner Ray Kelly praised Estrada.

“I want to commend Office Estrada, who had the presence of mind to focus on the man with the gun, and the courage to chase him down and capture him,” Kelly said.

But Estrada — who came from the same hometown as Figoski — West Babylon, LI — remained devastated over his partner’s sudden death, pals said.

“He couldn’t believe that his partner, who was the nicest guy in the world and the best cop, who had taught him so much, was dead, was gone,’’ one source said.

Another friend said Estrada can’t stop worrying about Figoski’s four daughters.

“All he kept talking about was Pete’s kids, saying, ‘Who’s going to take care of Pete’s kids now? That’s all Pete cared about,’ ” the police source said of Estrada, who was hospitalized with a sprained right shoulder.

“He was distraught. Most of the time, he just stood there with a blank stare on his face.

“He tried to remain strong, but there were numerous times when tears welled up in his eyes.”

Estrada, a married father of three, joined the NYPD in 1996, serving his entire career in the 75th Precinct, just like Figorski.

He married into a cop family: His wife Kathy’s dad, Richard Waszmer, is a retired Nassau County officer whose brothers were cops. Waszmer has a son who’s an FDNY paramedic and a nephew who’s a cop in Suffolk County.